Not Applicable.
Not Applicable.
1. Field of the Invention
This invention relates generally to sonar apparatus and in particular to sonar arrays used underwater.
2. Background of the Invention
A ship, for example a military ship, can tow an array of sound receiving hydrophones arranged as a passive towed array. The passive towed array, in conjunction with sound receiving and signal processing electronics, can detect sounds in the water that may indicate, for example, the presence of an enemy submarine.
In other arrangements, the ship can tow both the passive towed array of sound receiving hydrophones and also a towed acoustic projector, which together form a bistatic active sonar system. With this arrangement, the towed acoustic projector emits sound pulses. Each sound pulse travels through the water, striking objects or targets in the water, which produce echoes. The echoes are received by the towed array of receiving hydrophones. Therefore, an echo indicates the presence of an underwater object, and the direction from which the echo came indicates the direction of the underwater object.
In conventional bistatic active sonar systems, the towed acoustic projector is often deployed and towed separately from the towed array of sound receiving hydrophones. A conventional towed acoustic projector typically includes a sound source mounted within a large rigid tow body, for example in a conventional AN/SQS-35 tow body used by the United States Navy. The conventional towed acoustic projector is large and heavy. For example, the size can be on the order of forty-eight cubic feet and the weight can be on the order of 4000 pounds. The towed acoustic projector of this type is typically used to detect objects in deep water and at long ranges. Therefore, the towed acoustic projector is capable of generating sound having a high sound pressure level, for example 220 decibels relative to one microPascal at one meter (also written herein as dB re 1 xcexcPa at 1 m) in order to enable the system to receive echoes from and therefore to detect objects in the deep water at long ranges. This type of bistatic active sonar system is not well suited to littoral waters having a shallower depth.
The towed array of receiving hydrophones are often deployed and recovered through a hull penetrator below the ship water line. In contrast, in part due to its size and weight, the towed acoustic projector is deployed and recovered over the gunwale of the ship with winch and boom equipment. The large towed acoustic projector, which requires deployment over the gunwale of the ship, limits covert deployment and recovery. The deployment and recovery of the towed acoustic projector over the gunwale of the ship may also be unwieldy and dangerous during deployment and recovery in high seas.
Conventional bistatic active towed array systems are configured such that the acoustic projector is handled with equipment separate from equipment that handles the towed array of receiving hydrophones. Large handling equipment is needed to deploy and recover the towed acoustic projector. The large handling equipment requires a considerable amount of deck space on a ship. The large handling equipment is undesirable not only because of the deck space that it requires, but also because it presents a radar target having a large radar cross section to enemy radar systems.
It would, therefore, be desirable to provide a system that has an array of receiving hydrophones as well as a towed acoustic projector both of which can be deployed and recovered using a single set of handling equipment. It would be further desirable to provide a sonar system that has the array of receiving hydrophones as well as the towed acoustic projector both of which can be deployed and recovered through a single ship hull penetrator. It would be further desirable to provide a sonar system that is suited for operation in littoral waters having a relatively shallow depth.
The present invention provides a sonar array having both a receive array and a transmit array coupled to a single tow cable. The acoustic projectors used in the transmit array are capable of producing a high sound pressure level (SPL) while having a small size.
In accordance with the present invention, a sonar, array has a transmit array and a receive array to form a xe2x80x9creelablexe2x80x9d single line array. The transmit array has one or more acoustic projectors capable of generating sound and the receive array has one or more hydrophones capable of receiving sound. The one or more acoustic projectors are disposed on a transmit array axis, and the one or more hydrophones are disposed on a receive array axis. The receive array axis and the transmit array axis have a common axis, therefore forming contiguous line arrays, one for transmitting and for receiving. In one particular embodiment, at least one of the acoustic projectors can include a slotted cylinder transducer. In one configuration, the sonar array can be towed to form a horizontal line array having both acoustic projectors and hydrophones.
With this particular arrangement, the acoustic projectors and the hydrophones can be deployed and recovered from a single winch. The slotted cylinder arrangement allows each of the acoustic projectors to be relatively small and light, therefore, a relatively small winch can be used to deploy and recover the sonar array.
In accordance with another aspect of the present invention, a method for detecting underwater objects includes deploying a sonar array from a single winch, the sonar array including both a transmit array and a receive array. The transmit array has one or more acoustic projectors capable of generating sound and the receive array has one or more hydrophones capable of receiving sound, all arranged on a common axis. The method also includes recovering the sonar array from the single winch. The deployment and recovery can either be via a ship hull penetrator, or over a gunwale of a ship.
With this particular arrangement, the method allows deployment and recovery of the sonar system from a single winch. The deployment and recovery can be done covertly with a single ship hull penetrator.